Methods for manufacture and evaluation of vaccines and other products which may influence the course of infections caused by herpesviruses, including varicella-zoster virus (chickenpox and shingles) and herpes simplex virus types 1 and 2 (oral and genital herpes) are being studied. This includes development of methods to assess the purity of these agents (including freedom from contamination with other viruses), methods to evaluate the influence of these agents on viral latency and reactivation (a major safety and efficacy issue), and methods to attenuate products to minimize the safety risks of using products derived from pathogenic live viruses either as vaccines or in gene therapy. Human herpesviruses cause a variety of diseases which have a significant impact on the health of the nation. Varicella-zoster virus causes chickenpox in nearly all Americans, and when it reactivates from latency, causes shingles in approximately 15% of the population. Herpes simplex virus causes oral and genital herpes, and can cause severe, fatal infections, especially in neonates and the immunocompromised. Currently, over 100,000 Cesarean sections are performed annually in the U.S. to prevent neonatal herpes. Products which influence the course of these viral infections will have a dramatic impact on the health of the nation, and in particular, on women's health. Understanding methods used to construct and attenuate herpesvirus vaccines and gene-therapy products, development of methods to ensure their freedom from contamination with specific adventitious agents, and development of methods to assess the effect of these products on latent infection of these viruses enables reviewers to rapidly evaluate the consistency of manufacture, safety, purity, and efficacy of these products.